In my truck, the radio is in a bad location, right under the A/C controls. You can get a dash kit and a wiring harness to connect up to the factory connections for about 20 bucks a piece from you local car audio shop or wally-world... Match the colors of the wires on the wiring harness and the radio harness, and you're done..
depends for what year gm it is, because if its 2000 and up you need a relocation harness or a module, the module is more expensive, but less pain in the arse. basically u cant just cut the wires and wire the new head unit. u need to keep ur radio to control the chimes/air bags/abs etc etc
not to say that your truck is not different, but all I did with mine was the wiring harness and call it a day. the radio dumps it signal directly onto the speaker wires with nothing in between from the factory. In my saturn, it's the same way..but I have seen cases where there is an in-between, notably in my uncle's grand caravan where he had the upgraded audio, and the amps for the speakers were actually mounted on the speakers... if there's anything else I can do to help you, please ask.
according to what I saw on a couple different sites, the mid-90s radios have the actual amps and stuff in a separate box hidden and the "radio" is just the controller for it, but for an '89, I dont think they did that, espeically if I had the "upgraded" stock radio of '91, and it was all self-contained. Are you having a problem in installing your reciever, where everything's hooked up and nothing's coming out or what? If the harness fits an aftermarket wiring kit, you should have the end of the chain, with nothing in between.
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